Problem: Which of these numbers is prime? ${41,\ 49,\ 55,\ 77,\ 96}$
Solution: A prime number has exactly two factors: 1 and itself. The factors of 41 are 1 and 41. The factors of 49 are 1, 7, and 49. The factors of 55 are 1, 5, 11, and 55. The factors of 77 are 1, 7, 11, and 77. The factors of 96 are 1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, and 96. Thus, 41 is a prime number.